The proposed research extends our studies on the relationship between chromosome structure and organization and chromosome function. Monoclonal antibodies directed against different portions of histone Hl will be generated in order to precisely map the sites at which Hl interacts with purified nucleosomes and with intact chromatin fibers prepared to preserve higher order organization of the material. The electron microscopic in situ hybridization procedure we have developed will be extended to the hybridization of cloned genes to nascent transcripts associated with these genes in a direct approach to questions of primary transcript size and RNA processing patterns in eukaryotes. The identification and arrangement of components in constitutive heterochromatin will be continued in order to define DNA sequence specific-protein interactions which may be involved in the association of chromosomes with the mitotic apparatus and with the transcriptionally inert aspect of centromeres. As a corollary to these studies on constitutive heterochromatin, we will use the putative X-specific reiterated fragment identified in Bam Hl digests of human DNA to search for clones in the human genomic library containing this sequence. These clones will be used to test models of X chromosomes inactivation that involve modifications in the macromolecules which are components of the X chromosome. The overall goal of the above studies is to describe at biochemical and ultrastructural levels, features of transcriptionally active and inactive chromosomes.